1. Field of the Invention
The present invention relates to automated apparatus for ladling molten metal from a furnace to a mold and particularly to the stabilization of such apparatus as it moves through a downward path of motion.
2. Description of the Prior Developments
Apparatus for automatically ladling molten metal from a furnace into a mold are well known in the art and are commercially available under the name of Rimlock Ladlers, for example. Although these ladlers generally function well, a problem arises when the ladle is required to move in a downward direction. In this case, the electric motor which drives the ladle arm must act as a break to prevent the ladle from accelerating downwardly.
If the ladle is allowed to fall quickly downward under gravity, the molten metal carried by the ladle will be sloshed about at its abrupt end of travel. This is most undesirable insofar as any turbulent motion induced in the molten metal encourages the formation of oxides which create stress risers in the cast end product.
One approach to avoiding such turbulence is to operate the ladle at a relatively slow speed. Unfortunately, slow speed operation of the automatic ladler causes a drop in production rates as well as a significant drop in temperature of the molten metal carried by the ladle from a furnace to a mold.
Temperature loss in excess of 50.degree. F. in the molten metal is typically accounted for by raising the temperature of the metal in the furnace by 50.degree. to 100.degree. F. This also has a drawback since higher melt temperatures also facilitate the formation of oxides.
Although existing ladlers can be adapted to produce a downward path of motion, the negative load applied to the electric motor driving the ladler during such motion causes the motor to "hunt" or rapidly reverse direction. This hunting results in a jerky movement of the ladle arm and thereby induces turbulent motion in the molten metal carried in the ladle.
Again, such turbulence fosters the formation of oxides in the molten metal. In the case of a piston casting operation, molten aluminum silicon alloys quickly form highly undesirable aluminum oxides in the melt.
Accordingly, a need exists for an automatic ladler which provides smooth motion throughout its travel and which prevents the ladler drive motor from hunting and jerking the ladle arm during downward movement of the ladle arm. A further need exists for such a ladler which may be operated at high production rates and which minimizes the loss of temperature in the molten metal during its travel from a furnace to a mold.